Perry will win the nomination, and the Presidency, if Palin stays out.
If Palin jumps in, she’ll split the conservative financial support and vote, and Romney will take the nomination, and the Presidency.
Bear in mind that the above predictions are made by one who has supported Phil Gramm, Bill Frist, and Fred Thompson for the GOP Presidential nomination in prior years.
Last time around McCain didn't win the nomination. He didn't win anything.
What happened was the conservative vote got split up between candidates more conservative than McCain. McCain won by default.